1. Field of the Invention
The present invention relates to a signal transmission apparatus for transmitting signals between a control unit and a plurality of signal terminal means.
2. Description of the Prior Art
In an elevator system, a control unit is installed in a machine room, and signals are transmitted between the control unit, platform buttons provided on each of the floors, and cage operation buttons on a board installed in the cage. The machine room is usually located just above the elevator path. The platform buttons and the cage operation board buttons, which are signal terminals, are located more remote from the control unit as the number of the floors increases. To facilitate the connection and reduce the complexity of the wiring between the control unit and the signal terminals, there has been employed an apparatus which transmits signals in series on signal lines instead of transmitting signals in parallel through such lines.
FIGS. 1 and 2 illustrate a conventional signal transmission apparatus employed for an elevator system in which signals are transmitted in series.
In the drawings, reference numeral 1 denotes a control unit which is installed in a machine room of the elevator system, and which generates clock pulse signals and reference signals to register a platform call and a cage call. Reference numeral 3 denotes a signal line for transmitting clock signals 3a that are generated maintaining a constant period (for example, 500 microseconds), 4 denotes a signal line for transmitting platform call signals 4a, 5 denotes a signal line for transmitting platform call registration signals 5a, reference numerals 61 to 69 denote platform buttons (up-call buttons and down-call buttons are not specifically shown) of the first to ninth floors, 71 to 79 denote platform call registration lamps that indicate the registration of platform call, 81 to 89 denote memory units consisting of D-type flip-flop circuits which are installed on the first to ninth floors, and to which the signal line 3 is connected through the terminals CL, 91 denotes a signal line which connects the control unit 1 to the memory unit 81, and which transmits a reference signal 91a that assumes the high level only for one period (inclusive of a delay of a short period of time) of the clock pulse signal 3a, 92 to 99 denote signal lines which connect the memory units 81 to 89, and which transmit reference signals 92a to 99a (signals 95a to 99a are not diagramed) that assume the high level only for one period (inclusive of a delay of a short period of time) of the clock pulse signal 3a, successively, being delayed in time, 111 to 119 denote D-type flip-flop circuits (hereinafter referred to as memory units) of which the terminals D are connected to the signal line 5, of which the terminals CL are connected to the terminals Q of the memory units 81 to 89, and of which the terminals Q are connected to the platform call registration lamps 71 to 79, respectively, and reference numerals 121 to 129 denote AND gates of which the input sides are connected to the signal lines 92 to 100 and to the platform buttons 61 to 69, and of which the output sides are connected to the signal line 4.
Reference numeral 101 denotes a signal terminal means consisting of the platform button 61, signal lamp 71, memory 111, and AND gate 121. Similarly, reference numerals 102 to 109 denote signal terminal means of the second to ninth floors.
Next, the operation will be described below.
If a clock pulse signal 3a is applied to the signal line 3 and if a reference signal 91a is applied to the signal line 91, the output 92a at the terminal Q of the memory unit 81 becomes an input 91a to the terminal D at the time when the input 3a to the terminal CL is rising. Therefore, the output 92a assumes the high level for only one period of the clock pulse signal 3a when the reference signal 91a assumes the low level. Similarly, the reference signals 92a to 94a, . . . , assume the high level successively being delayed in time as shown in FIG. 2.
Here, if the platform button 62 of the second floor is depressed, output of the AND gate 122 assumes the high level when the reference signal 93a assumes the high level, and is transmitted as a platform call signal 4a to the control board 1 over the signal line 4.
If the platform button 63 of the third floor is depressed, output of the AND gate 123 assumes the high level when the reference signal 94a assumes the high level, and is transmitted as the platform call signal 4a over the same signal line 4. Even when the platform button 62 of the second floor and the platform button 63 of the third floor are depressed simultaneously, the platform call signals 4a are transmitted in series over the signal line 4, since the clock signals 3a have a very small period. This operation is repeated successively to obtain the conditions of the platform buttons 61 to 69.
As a predetermined number of pulses are sent as clock signals 3a, the data are all collected. These signals are processed by the control unit 1, and are registered as a platform call.
The thus registered platform call registration signal 5a is transmitted through the signal line 5, whereby the input assumes the high level at the terminal D of the memory unit 112. In this case, since the signal 93a of the high level is input to the terminal CL of the memory unit 112, the output at the terminal Q assumes the high level, and this level is maintained. Therefore, the platform call registration lamp 72 of the second floor turns on, indicating that the platform call is registered. Similarly, the platform call registration lamp 73 of the third floor also turns on.
The registration lamps 72, 73 can be turned off according to the same procedure as described above, though not described here in detail. That is, if the platform call registration signal 5a of the signal line 5 is rendered to assume the low level when the cage of the elevator has arrived at the second floor, the output at the terminal Q of the memory unit 112 assumes the low level when the reference signal 93a rises, and the platform call registration lamp 72 of the second floor turns off. The same also holds true for the registration lamp 73 of the third floor.
Namely, only four signal lines 3 to 5, and 91 are required to connect the platforms to the machine room.
However, although the number of signal lines can be reduced, this system is seriously affected in case, for instance, the lines are broken. For example, if the memory unit 82 becomes defective, and the signal 93a assumes the low level at all times, the memory units 83 to 89 all assume the low level, and the call is not registered by the platform buttons 62 to 69. Further, if the memory unit 81 becomes defective, the call is not registered by the platform buttons 61, 62, . . . , and the elevator is placed out of service.